Mining method



P. B. BUCKY MINING METHOD Jan. 2, 1951 s sheets-sheet 1 Filed June 22,1946 FIG. 2

,INVENTOR: Phlllp B. Bucky ORNEYS.

Jan. 2, 1951- P. B. BUCKY MINING METHOD Filed June -212, 1946 3Sheets-Sheet 2 INVENTOR Phili B. Buck Byfwgmwlpmm y #M AT ORNEYS P. B.BUCKY .MINING MTHOD Jan. 2, 1951 :s sheets-sheet s Filed June 22k, 1946INVENTORI Philip B. Bucky BY: Qu ad @mi fi@ ATTORN YS Patented Jan. 2,1951 UNITED STATES rATENT OFFICE MINING METHOD Philip B. Bucky,Larchmont, N. Y. Application June 22, 1946, Serial No. 678,614

13 Claims.

This invention provides a new and economical method for mining ore thatmay be used for Working both underground deposits and those that crop onthe surface. The new method is particularly satisfactory for miningorebodies in regions where the orebody and the ground in which it occurstends to spall or fail into open spacesy and where wall failure dilutesthe broken ore with waste rock. However, it may be used for mining anydeposit where it is advantageous to provide support for the groundduring or after mining operations. The invention further provides forobtaining improved ore fragmentation in the stope being mined, and forwithdrawing the ore from the stopes without dilution by waste rock orll.

The preferred embodiment of the new method may be termed the shrink-fillmethod of mining, as it involves rst breaking the ground by a modiedshrinkage method of stoping, and then introducing Waste ll at the top ofthe stope as the fragmented ore is withdrawn from the bottom and as itsupper surface subsides within the stope. However, other methods thanshrinkage methods may be used, in appropriate cases, to break theground.

Many dilferent methods for extracting ore from mineral deposits areknoWn and employed. The choice of the particular method to be used inmining any given ore deposit is mainly a matter of selecting the mosteconomical method to which the deposit lends itself, taking into accountsuch factors as richness of the ore, the ease with which it may bebroken to permit its withdrawal, the size of the deposit, and themechanical strength of both the orebody and the ground within which thedeposit occurs. Shrinkage methods of mining often are employed. Atypical shrinkage method involves digging into the deposit at a, depthbelow its upper surface, and breaking the ore down from the roof of theworking space. If the surrounding ground is strong, it is generallysu'icient to continue breaking ore from the roof of the stope andwithdrawing the broken ore from the bottom of the stope at the properrate to provide working space for the men until the upper limit of thestope is reached. During the ore-breaking operations the upper surfaceof the broken ore serves as the floor of the working space, andwithdrawal of the broken ore is regulated to maintain a working space ofproper height. Thereafter the broken ore is simply withdrawn from thestope, leaving an open cavity underground.

If the surrounding ground is not suciently (or cavity) is formed withinit, some method of supporting the ground and/or preventing dilution ofthe ore must be provided. This is also important in regions whereprecautions must be taken against ultimate surface subsidence, becauseeven strong ground may ultimately cave into open emptied stopes.

Numerous methods for supporting the surrounding ground from which orehas been mined are known and employed. Some such methods involveextensive use of timbers to support the ground during mining operationsand subsequently. Often the spaces between the timbers are lled withwaste rock after the ore has been extracted to provide permanent supportfor the ground. Considerable handling of small batches of broken ore andlill material usually is required in mining by these methods. Thetimbering and the handling of ore and ll make such methods expensive,and consequently they are generally used only for mining high gradedeposits.

In the so-called cut-and-ll method, the ore is usually broken from thestope roof (as in the typical shrinkage method described above), andafter one cut of ore has been taken from the roof of the working spaceand has been withdrawn by shovelling, scraping, or other means, waste llis introduced to take the place of the ore removed and to raise thefloor of the Working space high enough to permit another cut to betaken. This method saves the expense of timbering, but involveslaborious handling of broken ore and waste fill Caving methods whichinvolve breaking the ore simply by allowing it to cave into an undercutopening are generally the most economical methods for undergroundmining, but such methods can be used only where the ore is of suchcharacter as to break properly by caving, and where surface subsidenceof the ground is not important.

The new mining method provided by the pres- 'ent invention is generallyapplicable where shrinkage, cut-and-ll, block caving, and similarmethods have heretofore been employed, and is also applicable in manyinstances where extensive timbering, or timbering and iill, has beenconsidered necessary to support the surrounding ground.

Briefly the new method comprises breaking the ore throughout the heightof a stope within an orebody and withdrawing the broken ore by gravityflow through a chute at the stope bottom. In a preferred embodiment ofthe invention, the ore is broken down from the solid mass of ore in 3place while the space between it and the previously broken ore is verymuch smaller thanv ha been maintained in heretofore known miningmethods. In general the upper surface of the column of broken ore in thestope is maintained sunciently close to the lower surface of theoverhanging unbroken ore so that any space therebetween is no greaterthan will be filled substantially completely by material broken in thesucceeding, 'blasting (orefbreaking) step. Advantageously, i'some casesthe upperl surface'of the broken ore may at all times be maintainedsubstantially in contact with the roof formed 'by the overhanging massof unbroken ore. In this manner, the force of the blasting operation bywhich the solid ore is broken also 'contributes to further fragmentingthe underlying already broken ore. The drilling andother mining oper'-ations are conducted from working positions within a rathersmallamanway, so that working onditions are` safer than is possible whenthe miing'operatidns 'are conducted in relatively large underground openworking spaces.

VAlflfterthe ore has been broken throughout the height of the stope,waste ll is added at the t"9D of theA stope at v'substantially the samerate as thebro'len ore4 is withdrawn through' the chute at the bottom ofthe stopejand asv the upper surface of theI broken ore subsides therein.Thus the )st'ipe'v 'maintained substantially full ofbroken'inateriall'tore or fill) at all times.

o "Withdrawal 'offthe broken ore through the chute 'at the` bottom,ofthe stope is continued, with continuing addition of waste ll at thetop of the stope', until'theinterface beween the orez andthe wastereaches the level'at which the angle' from the ore withdrawal chute tothe laterally most'rmte part of the ore-ll interface `is less tljran'A'about '10 to the horizontal. Further. withdrawals of ore by gravity owthen vare'n'iost advantageously. made through another chute locatezd'ata point such that said angle is appreciably greaterthan about 70.

The new methodl is generally more economical andin its preferredembodiment may be ernployed with greater safety than is generally thecase'with 'heretofore known mining methods such as those brieflydescribed above. The new method is `e..pp' licable'to orebodies whichdip but gently from the horizontal and equally to orebodies which dipsteeply. It may be employed successfully in mining lange orebodies ofgreat width and length,l as well as in mining relatively smallorebod'ie's. VIt is especially useful in mining ore from depositsoccurring: in ground which is weak and tends to. cave or spall in openstopes, and where provision must therefore be made to avoidoontamination of the ore and to provide supportfor the ground, but itmay also be used in regions where the ground is strong. The new miningmethod is peculiarly eifective for preventing rook bursts, a typeofground failure that often occurs in open mining cavities in strongground. However, the new method may be employed in mining ore fromdeposits in strong ground, even where'rock bursts donot occur, in orderto insure permanently against caving and surface subsidence after thedeposit has been mined out.

The invention is described in some detail be low' with l reference "tothe embodiments diagrammed in the accompanying drawings. Theseembodiments illustrate characteristic and pre- 4 be made in adapting thenew method to particu; lar ore deposits. In the drawings,

Figs. 1, 2, 3 and 4 show successive stages in mining ore by the newmethod from a steeply dipping, rather narrow deposit; and

Fig. 5 shows an adaptation of the new method to the mining of ore froman essentially horizontal deposit of considerable extent that outcropson the surface.

In theembodimentshown in 'gss 1 to 4, ore is being minedby the new methofrom a steeply dipping deposit or orebody I0. Preparatory to mining theore, crosscuts Il are driven from the mi' e shaft (not shown) to theorebody. Level dril s l2 also are driven alongside the orebody atvertical intervals of say 50 to 300 or more feet to permit ready aocessto the orebody. Crosscuts 3 extend out Afrom 'these level drifts intothe orebody. Ore chutes I4 are driven upwardly from the level drifts l2into the ore deposit at an angle preferably somewhat greater, than tho,angle of repose. of broken orefrom the orebody.

After the preliminary de velopmenh'theore.in r

the stope that has been markedE out by, the development work is brokensu'iciently 'so vtljatit may liow by gravity through .the chutes .MIinto mine cars for transporting it. to the mine shaft, through whichitis hoisted tothe surface. The Chutes "|24 are 0f -g'ursa pronged withthe usual gates to control the flow of broken ore .from the stope, i'

Breaking the ore maybe accomplished in, any desired fashion. -It. *forvexamplal broken by the conventional shrinlagegmzethod,deseribed above,or if the fore. sldf proper, aving, qualityfit may be broken by a cavingmethod. Generallm however, I prefer to employ the modified and'vimproved shrinkage method illi'lstrated in" the drawings and` describedbelow. Figs. 1 to l showsuccessive. stages in the. progress of.ore-breaking operations. Enr purposes, of

illustration, it-is assumedthat the ore is to-be broken in a series ofstones, arrang'edone above the other, and each of about the height fromone level drift l2` to the next 'level drift above. In carrying out themethod, a raise l5 is Vr'st` driven along the foot wall of the orebodythroughout the height of the stope, from one working'level to the nextabove. As shown in Fig. 1, the. raise o l5 has been completed throughoutthehe'ight'of the upper stope and a considerable portion of the ore l5:in thisvstope has already been broken. The corresponding raise in thestope neigt beldv/,s in the course of being driven. upwardlyv .Tfheraises t5, provide .the working space from with-in which theore-breaking operations are conducted, and may be placed wherever, andin whatever numbers, most advantageous.forworkingfthe deposit. "Y nBefore breaking Ore Within a Stasera geen face at the bottom of thestope is 5ot`1ta-inerl, by excavating an opening IJ, s ay siate eightfeet in height. extending'. advantageously'from the foot wall to the.hanging wall thea-lengthof the stope. Drill holes l.8 thenaredrivenacross the orebody from the raise, I5 atan appropriate distanceabove the bottom surfape of the unbroken ore in the stope. The drillholes are loaded, tamped and fired to blast the ore down from the roof.A limited and controlled amount. of broken ore then is withdrawn throughthe chute I4. The amount withdrawn is considerably less than hasheretofore been considered,neo;ssary, and ingeneral is such that any,space. .thereby created b etween the @Per safes-e f=hebr1eersand subsidefrom the top of the stope.

the lower surface of the ovrhanging unbroken mass (such as-the spacesI'Ia in the upper and intermediate stopes in Figs. 1 and 3) is nogreater in volume than will be filled by ore broken in the nextsucceeding blasting operation. In some cases the amount of ore withdrawnis no greater than sumcient to create voids in the mass of broken ore,without lowering the upper surface of the broken ore substantially outof contact with the .overhanging roof of unbroken ore (as.

practical to the still unbroken roof of ore in place. This advantage isthat the force of the blast not only breaks ore from the solid roof, butserves also to cause additional fragmentation of the broken ore lyingdirectly below the roof. The improved fragmentation of the ore therebyobtained reduces any tendency for the ore to be blocked in the chutes bylarge lumps, and otherwise facilitates handling the ore underground. Italso facilitates crushing and grinding in subsequent preparation of theore for treatment to recover its valuable components. Another advantageis that the working space is within the confines of the raise I5. Themining operations can be conducted from this position with greatersafety than is possible if such operations must be conducted fromworking positions in an underground opening of substantial extent. Stillanother advantage is that the stope is maintained full or nearly full ofmaterial at all times, without such open spaces as normally are providedfor working purposes, so that the walls of the stope, and to aconsiderable extent the roof of .unbroken ore, are well supported at alltimes throughout the mining operations. Spalling of weak wallsand'consequent dilution of the ore, and rock bursts such as occur instrong ground, are thereby prevented.

The appearance of the workings after all of the ore has been broken inthe upper stope and as ore-breaking operations are commencing in theintermediate stope is shown in Fig. 2. Advantageously the roof I9 of theupper stope is shaped as shown in the drawings, so that it forms anlangle with the horizontal greater than the angle of repose of the flllmaterial subsequently to be introduced. The ore from this stope may nowbe withdrawn as required through the upper chute I 4, and may betransported to the mine shaft for hoisting to the surface.

Concurrently with or subsequently to breaking the ore in the upperstope, ore-breaking operations may be similarly carried out in theintermediate or lower stopes, as illustrated in Figs. 2, 3 and 4. Theonly difference in procedure in working in the lower stope, as comparedwith working in the uppermost stope, is that the orebreaking operationsin the lower stope are carriedfall the way up to the point of breakingthrough into the stope next above.

After the ore has been broken all the way to the top of the uppermoststope, continued withdrawal of broken ore through the chutes I4 willcause the upper surface of the broken ore I6 to Thissubsidencewillcreate an open cavity within the ore deposit. If this opencavityassumes substantial proportions, the surrounding ground,particularly if it is weak or tends to spall, is likely to cave into theopening thus created, mix with the ore, and lessen its value. Suchcaving may also render development drifts in the caved region unusableand tend to cause subsidence of the earth at the surface of the ground.Large openings greatly increase the hazard of rock bursts, and maypreventmining in adjacent unworked sections of the orebody.

To prevent such diinculties due to large openings underground, waste llis introduced into the stope through a suitable opening or chute leadingto the' apex of its inclined roof I9. The waste ll is supplied to thetop of the stope at substantially the same rate and in substantially thesame amount as broken ore is withdrawn through the chute or chutes I4and as the upper surface of the broken ore subsides within the stope.The amount of waste fill thus introduced is sufficient to maintain thestope in which Vthe ore has been broken substantially full of brokenmaterial (ll or ore) at all times. The ll and broken ore prevent cavingor spalling of the surrounding ground to any appreciable extent, whenthe ground is weak, and prevent rock bursts when the ore and surroundingrock are strong.

By forming the roof I9 of the stope at an angle greater than the angleof repose of the lll material, fill introduced at the apex of the roofwill ow out against the roof and provide support for it as well as forthe walls of the deposit.

Any available material may be used as ll. Barren rock from developmentdrifts, or tailings from a concentrator plant located near the mine,often are available and are well-suited for use as ll. The fill-may bebrought to the stope through the upper level drift I2 and crosscut I3,and may be dumped into the stope through waste chutes provided for thispurpose. If desired, such waste chutes may extend all the way to thesurface of the ground, so that fill may be introduced into the stopedirectly from the surface.

I have found that the waste fill may be added directly on top of thebroken ore, and that as the ore is withdrawn through the chutes withconsequent subsidence of the interface between the waste fill and ore,little or no intermixture of the waste with the ore will occur until theore-fill interface approaches the chute more closely than apredeterminable distance. This distance is the height the interface mustbe above the ore chute so that the angle from the chute to the laterallymost remote part of the interface is 70 (more or less, as bestdetermined by experiment). When withdrawing ore that has been brokenthroughout the height of several successive stopes, as illustrated inthe drawings, I therefore prefer to regulate withdrawing of the ore asfollows:

When the interface between the ore and ll has subsided in the upperstope to a level where the angle from the upper stope chute to thelaterally most remote part of the interface is no more than about '70 tothe horizontal, fwithdrawal of ore through that chute. is discontinued.The upper limit of the dotted line 20 in Fig. 3 indicates the level ofthe ore-fill interface at the time when withdrawal of ore through theupper chutes I4 is discontinued.

The angle indicated above to be about 70 does not under allcircumstances have precisely this value. It may vary considerably oneway or the other, depending in general on the now charac tetsties; of;tbehrokenf oie, but ordinerlie it. is.

chuteyinquestion as4 the. interface 'subsidesfeveniyf In the case -of a,Wide stone; served.- bvseveral chutes on the same level, thelaterallymost remote? part, ottbeiinterfaee in thedirection f anotherchute-may, bel taken aspbeing; along a lineemidway between;the chutes.

After the, interface between theIY ore and waste ll has-.reached theVlevel belowA which it is inadvisablesto continue-withdrawing orethrouehthe uppenchute l I 4,1, further withdrawal Aofthev .lonokenoremay' be; eiectedthrough the; chute. at the bottom of the; nextglowerstope'lthe intermediate stone. as shown, in the drawings), When thesubsiding interface between the 4 ore and; ll reaches the level-(indicated by thegupperylimit oigthevdotted line 2l in Fig. 4) wherethe-angle from this chute to thelaterally. vmost; remote partofatheinterfacejs again '70moreor less, withdrawalV through-nthe,intermediate, chute is. discontinued,- and-furtherwithdrawalzisfeffected as through the-chuteat thetbottom of the.lowermost stope, after` the solid portionbetween stopes is fragmented;

As'. a result-:of the. aboverdescribed procedure. for withdraw-ingthisore,v the -subsiding interface between-.the ore and added retainssubstantiall'ytthe.I shape.v of-the: top of Vthe. upper stope aftiwhichthe;.ll' is, added, untilthe.v interface reaches the..y level 4at* whichi the angle.- from, the lowerrnosti chute.. to the*A laterally 1mostremote part of. the :interfaceI isabout 70.

In .withdrawing the -ore .through the; chute or chutes at the bottom vof:the lowermoststepe,l the withdrawal may be continuedeven after theinterface between the-ore -and-ifill hasl subsided to below the level`.corresponding `to thatfatwhich withdrawal operations.- through .thehigher level chutes. were. discontinued... Indeed, withdrawal through.4thelowermost chute may continue until waste illxshowsinthe orefchute,which then indicates-that,substantially all .of :the-ore has. beenwithdrawn from thel stope, and that it contains little but-waste ll.Therewill, however, remain a:.vol11me.122 e of ore (occupying. theregion .below tha-dotted line. 23-iin Fig. 4), which cannotzbe withdrawnbygravity flowthroug-h the'lower-most chute i4; This-tore,- andianysmalLunderlying massfofiunbroken ore, maybe either left inzplaceonminedfbyspecialmethods.

Thenew mining methodas describedaboue may be used to. mine concurrentlyseveral stopes within the-same. ore,bod`\7. For example; in mining asteeply dipping orebody such as illustrated i'n- Rigs. 1 izo-4, miningoperations mayibeproceeding in stopes ait-several ,levels at the. sametime; In this way, the rate Aat -which ore-is mined from the, depositmaybe-increasedi The height off'the stope to be `:worked may-.finfactbe. determined in part=from the numberof different stopes thatiit isdesired to lworkeoncurrently for, purposes-of obtaining.aflargedailyoutput-of-.ore`

Fig. 5 illustrates an adaptation off the new method to miningconourrentlyin several adjacent stopes-in -anessentially horizontal.orebody which outcrops on. the-surface-- As :shown in this figure. theorebodytis of -heig-ht Hfand adjacent iopessl; 32,-' 33 and-34eme invariousstages'ot Werktage. eimainhaulaeewar sdrvenin the reels 44beneath-the orebodxt and f. ore chutes- 3 64 extend :from it :int othe.1 orebodyi- StopeA 34; shown in the drawings has been markedfputand-prepared for mini-ngl by driving-:a manway-raise- BJ :throughthe-stone.V and opening the: ore-chutes :36;but ore-breakinghas net befeuniinthis-stope.. In istopef?. .ore-isbeing broken by-z a..sl1rinkage-. methode of. the characterv dee scribed.- previously.'Ihefworking spacefr orebreakingoperationsris in@ the manway raises;3.1: Drill .holes 38. are. made fromsetups in the; raises 31; (they. maybeemade by long-hole. diamond drills). to :permitxplacing Loi;thefexplosive: charges in'. the overhanging solid ore. Broken ore 45;` iswithdrawn from ,the stope through the chutes-w35 asrequiredto createvoids-.inthe mass ofi-broken ore.- aiter. eaohiilast,4 as. described:above.Y The bottom oteaehstope is :shownformedl witha sloping bottom so`thatthe ore'1 may feedtdireotly into .chutesandinto the earsor conveyoron the main .haulage drift 35i stopezrisfshown as it appears aftertheore has been-.broken all the wayv-to the surface-and initial additionof liill has been-:placed on top. `of it, During subsequent operationsAin this .stope,

ore is. withdrawn by lgravity ow through chutes 3=leadingto themainhaulagewaydi Waste ll is introduced atithe-surfacel at substantiallythe samerat-eas broken ore-is withdrawn,A so as to maintain A`the-storieAfull-atv all 'times of broken material.

The-left-lrandstope I is shown 'in Fig. 5 as it appearsafter' nearl-yf.all of-the-broken-ore therein has--been-Withdrawn throughthe orel chutes35 communicating with=-themain haulageway; Waste1lhas= been introducedat substantially the lsame rate as broken oreV has been withdrawn, sothat the stope has been maintained full of broken-- material. The fillisintroducedrdirectly ony top of` the# broken ore, as I havefound thatno -timbervrnatting or-other` separating means at the interface GG ofbroken ore and il is necessary to prevent-dilution oftheore by the ll asthe ore is v.vlthdrawn and as the interfacel $9 subsides within thestope. In fact; Withdrawal-lof theore results in quite even subsidenceof the interface et' between the broken ore and iili, withvv little'orno intermingling-of these broken materials. After completion of theore-drawing operations (when wast-eA appears in the ore chute), somebroken ore 4i and some solidore 42 may. still remain in the stope (asshown for examplein stope 3i) These residual volumes fof ore are small,and maybe left in place or may be mined-by special methods.

An important feature of' the stoping operations illustrated inlii'g 5'isthe maintenance of partitions 43.0 f ore in' placeb'etweerithe stopes3f, 32, 33; etc, These partitions (which consti? tute only a smallportion of the o're body) pref vent'lziroken ore in one stope from'intermingling by'cross flowwithwaste fill added to an adjacent stope,with consequent dilution of the broken ore. In theabsence of partitions,cross ilowwill occur both during the orefbreaking operationsandsubsequently, if the mining operations in one stope aresubstantially. farther advanced than in, the vadjacent stope. Inaddition to resulti'ng in dilutionof the broken ore, such cross flow.would seriously hamper conduct of the miningvoperations. The partitions43, besides preventing cross flow of ,fill 'and broken ore, serve aspillars .for helping support the ore. in place whileore-breakingoperations are' in progress.

1 'If it is desired to recover all of the ore from the orebody and notleave any ore in place as part-itions, it is often possible to erecttimber partitions in the course of the ore-breaking operations. Whenthis is done, substantially all of the ore in the deposit may be brokenand recovered,

but in such event the distance between broken ore and roof must beincreased and drilling may take place in the stope (as in conventionalshrinkage-stoping operations). It is also possible to add cementingmaterial (such as Portland cement) to the fill material at the stopeboundaries, to enable the fill to stand, and when this is done miningoperations may be conducted in a subsequently worked adjacent stope soas to break and extract al1 of the ore up to the cemented fill. Thisprocedure also avoids the need for leaving any partitions of ore inplace.

To insure substantially complete extraction of the broken ore from thestope when mining in accordance with the method described herein, it issometimes advantageous if the bottom of the stope inclines downwardly toa bottom apex at an angle best determined by experiment, but whichapproximates 70 to the horizontal. The ore chute should of coursecommunicate with the stope through this bottom apex. This angle isindicated in Fig. 5 as that of the boundary between the residual volumeof broken ore 4I and the added waste ll in stope 3l. So long as theinterface between the broken ore and added fill is suflciently highabove the bottom of the stope, it will subside substantiallyhorizontally as the ore is withdrawn. Near the bottom of the stope,however, the broken material, if followed by ll, funnels to the orechute at an angle of about 70, more or less. As the substantiallyhorizontal interface between the broken ore and fill enters the regiontoward the bottom of the stope where this funneling occurs, it toowillrbegin to assume a funnel shape with its apex pointing downwardlytoward the ore chute. If the bottom of the stope is horizontal, or lessthan the above stated angle, some broken ore then will remain in placewhile waste fill funnels through it to the ore chute. By sloping thebottom of the stope at 70 or such other angle near 70 as is indicated byexperiment, there will be no opportunity for this funnel of broken oreto form and in ccnsequence no broken ore will be left in the stope. Withstopes having a properly7 sloped bottom, the appearance of waste ll inthe ore chute is a sign that essentially all of the broken ore has beenextracted. If the ore is of sufficient value, the

sloping bottom of the stope may be formed entirely in the barren rockunderlying the ore deposit, and all of the ore may then be broken andextracted.

The new mining method herein described, by providingV for addition ofwaste fill at the top of the stope as broken ore is withdrawn from thebottom, greatly simplifies the mining operations. In contrast to thecut-and-ll method of mining, the new method avoids the need for muchhand mucking or scraping of ore, and handling and evening of added ll.Yet it is generally applicable to mining in orebodies adapted to thecut-and-ll method. It is also applicable in some cases to orebodiesheretofore mined by stopes heaviy timbered to support the surroundingground. When adapted to such orebodies, the new method saves greaty onthe amount of timber required and on the cost of installing the timber.

Once stoping operations reach the point where rlll is introduced, oremay be withdrawn steadily and at any desired rate from the stope'untlvirtually all of the ore has been extracted. No heretofore known methodthat provides adequate support for the surrounding ground has achievedthis advantage. In general, the economies effected in mining operationsconducted in accordance with the invention are greater than can beachieved under comparable conditions by any other method which provideseffective and permanent support for the surrounding ground.

It is of course 'evident that the advantages of some features of theinvention may be had without making full use of all of the features ofthe complete new method. For example, it is possible to derive thebenefits of adding ll at the top of the stope while withdrawing ore fromthe bottom regardless of what method of breaking the ore was employed.Hence if desired ordinary shrinkage stoping, caving, or otherconventional orebreaking procedure may be followed. Similarly Y thebenefits of the improved ore-breaking procedure herein described may beobtained without adding fill at the top of the stope after completingthe ore-breaking operations, if there is no objection to leaving an openempty stope underground.

The significant features and advantages'of the new mining method hereindescribed may be briefly summarized as follows:

The modified shrinkage method for breaking the ore that isadvantageously (but not necessarily) employed in connection with theother features of the invention is principally characterized bywithdrawing a minimum amount of ore through the chutes after eachblasting operation. The amount withdrawn is considerably less thanheretofore considered necessary and in many cases need not result inlowering the upper surface of the broken ore substantially out ofcontact with the overhanging unbroken ore. It is desirable to have thedistance between broken ore and unbroken roof as little as possible.With this procedure the following benets accrue:

1. The men always work in a small relatively safe space, such as theraises shown in the drawings, and not under a large open span in astope. In addition, a minimum number of openings is required to work anorebody by the new method, and the openings required are of minimumdimensions. This makes the new method particularly safe, and reduces toa minimum the amount of expense involved in Ventilating and cooling themine workings.

2. The broken ore not only provides support for the walls of thedeposit, but to some extent may also provide support for the roof ofunbroken material.

3. The force of the explosive is not only expended in breaking ore downfrom the solid mass, but also serves to further fragment the brokenmaterial lying in the stope. In consequence, less secondary breaking ofore in the mine (as required, for example, to open plugged chutes) isnecessary, and crushing of the ore taken from the mine is simplified. Inaddition, the ore broken down from the roof is better fragmented,because it is broken against the jagged upper surface of the previouslybroken ore.

The addition of waste ll at the top of the stope after all of the oretherein has been broken, at substantially the same ratefas broken ore iswithdrawn at the bottom of the stope, is the characteristic feature ofthe invention for providing support for the surrounding ground aftercom- 121 pletion ofthev orebreakingk operations. procedure leads. to thefollowing advantages:

1. Ample support. is providedl for the ground without the-need forexcessive handling ofwaste lill-and without the` use oftimbers.

v2. In weak ground, the` support providedby the added iill preventsspalling of waste material from the walls ofthe deposit, and preventscaving ofv the ground,- which if it occurred woud result in diluting andlessening the value .of the broken ore.

3: In strong ground, the added fill prevents rock bursts that are apt tooccur in large underground openings, especially at considerable depths.The new procedure for adding lill, especially when used in conjunctionwith the herein-described procedurefor breaking the ore, makes itunnecessary to form any large open spaces underground at any stage of-vthe mining operations, and-so makes it feasible to conductminingoperations atv muchgreaterrdepths than have heretofore beenpossible in ground-that is subject to rook-bursts.

4: The added ll, of course, is highly effective for-preventing surfacesubsidence during or after mining operations.

' The adaptation of the new miningmethod described in conjunction withFig. 5. has the following particular advantages:

1. It makes it possibletominein a considerablenumber of closely spacedstopes and enables the mining operations in each stope to proceedindependently offthosein adjacent stopes. Most of the load involved insupporting the surrounding ground is borne bythe' broken ore and addedlll, soA that the partitions of ore in place may be. very thin. Ifdesired, even thesev thin partitions may be extracted by erecting timberpartitions-or cementing theadded fill along theboundaries of the stope.

2. If applied to underground mining, this method permits substantiallycomplete' extraction of ore from large and extended. ore bodies withoutcaving or surface subsidence.

This

3. When applied to surface outcropping deposits, as particularlyillustrated in. Fig. 5, the new method may be used to supplant open-cutmining, or may be used in conjunction with opencut mining to remove thevaluable ore along the side slopes of the open cut without having to rermove large amounts of waste ground or overburden to prevent caving. ofside slopes into the open cut. This of course' results in increasedrecovery of ore with decreased mining of waste material from the sideslopes.

Most adaptations of the new method to either underground or surfacecropping deposits leadto the following general advantages:

1. A Working pattern for the orebody that is independent of the numberof solidV block faces in juxtaposition may be developed.

2. Economic Working of orebodies which when cavedl produce fragments ofa size difficult to handle underground is facilitated.

In general, the new method may be applied advantag'eouslyv to replace,or to be used in conjunction with, such heretofore known mining methodsas shrinkage stoping, cut-and-ll stoping, top slicing, sublevel caving,block. caving, and open-cut mining.

I-claim:

l. The method ot mining ore from an underground deposit in groundrequiringsupport which comprises breaking the ore in a stope'within thedeposit. sufficiently to withdrawal from said stope bygravity flow,forming thexroofo the stope at an angle to the horizontal substantiallyas great as the angle of reposeof. available waste ll, introducing suchwaste fill into said stope. at the top thereof, and continuouslysupplyingsuch iill to the stope in substantially the sameamount and atsubstantially the same rate as broken ore subsides from the top and isAwithdrawn from the bottom of said stope, whereby the walls and roof ofthe stope are at all times supported by broken ore or added fill.

2. In the mining of ore from adeposit in which ore in a stope in thedeposit is broken and the broken ore is withdrawn from the bottom ofsaid stope with consequent subsidence of its upper surface, theimprovement which comprises form.- ing the roof of the stope at an angleto the horizontal at least as great asA the angle of repose of availablewaste fill, and adding such. Waste fill directly to the subsiding uppersurface of the broken ore and continuingV the addition ofsuch waste llcontinuously in substantially the amount required to maintain said stopefull to the roof with broken material at all times.

3. The method of miningore from a. deposit which comprises marking oifwithin thedeposit a stope of substantial height; and ofA less Widththanthe width of the deposit, breaking the ore within said stope andwithdrawingV it from the bottom thereof, forming the roof of the stopeat an angle to the horizontal at. least asv great as the angle of reposeof available ll material, adding such waste fill at the top of the stopeat substantially the same rate as the upper surface of the broken oresubsides therefrom and in amount sudlicient to keep the stope fullv tothe roof at all times with addedA ll, similarly working a horizontallyadjacent stopewithin the deposit, and maintaining between the. stopes apartition capable of preventing admixture by cross flow of ll added toone stope with ore broken in the adjacent stope.

4. The method of mining ore from an under.- ground deposit whichcomprises breaking ore. in a stope within the deposit, withdrawing. thebroken ore from adjacent the bottom of the stope, forming the roof ofthe stope at an angle to the horizontal substantially as great as theangle of repose of available ll material, and introducing such Waste llinto the top of said stope through the apex of the angular roof thereofat a rate substantially equal to the rate at which broken ore iswithdrawn from said stope and as its upper surface subsides therein, theadded fillbeing at all time's maintained in substantial contact with theroof of the stope so as to provide support therefor as well as forA thestope side walls.

5. The method of withdrawing broken ore from an underground stope and`providing support for the surrounding ground which comprises withdrawingthe broken ore from the bottom ofthe stope and adding waste ll at thelto'p thereof directly to the upper surface of the broken ore, said Wastefill being added as the upper. surface of the broken ore subsides and,in amount sufficient to keep the stope substantially. full ofbrokenmaterial at all times, the added fill being at all times. maintained incontact with the. roof. of the stope so asv to provide support thereforas well as for the stope side walls. y

` 6. rThe method of mining ore from a deposit in ground requiring supprtwhich comprises forming a manway. extendingA upwardly through the heightof a stope within the deposit and, an ore chute communicating, with thedeposit adjacent the bottom of said stope, drilling from the manway intothe deposit above the chute, breaking the ore by blasting from the drillholes, withdrawing the broken ore through the chute only in controlledlimited amount such that voids are created in the mass of broken orewithout lowering its upper surface substantially out of contact with theoverhanging unbroken ore, and continuing breaking of the ore in saidmanner to the top of the stope, the stope below the unbroken ore beingmaintained substantially full of broken ore at all times duringore-breaking operations.

7. In a method of mining ore from a stope containing broken ore in thelower portion thereof and unbroken ore above, involving blasting orefrom the lower portion of the unbroken ore mass downwardly against saidupper surface of the broken ore, the improvement which comprisesperforming the blasting operation while the upper surface of the brokenore is in contact with the overhanging unbroken ore, whereby the forceof the blast further fragments the already broken ore as well asbreaking a further quantity of ore.

8. The method of mining ore from a stope containing broken ore in thelower portion thereof and unbroken ore above,lwhich comprises plas*- ingore from the lower portion of the unbroken ore mass downwardly againstthe upper surface of the broken ore, maintaining the upper surface ofthe broken ore at all times substantially in contact with the lowersurface of the overhanging mass of unbroken ore so that no extended openspace is permitted to form-between the unbroken ore and the underlyingbroken ore, whereby the blasting operation contributes to furtherfragmentation of the already broken ore, then withdrawing suicientbroken ore from the lower portion of the stope to create fresh voids inthe column of broken ore without creating any extended open spacebetween its upper surface and the lower surface of the still unbrokenore, and repeating the sequence of operations.

9. The method of mining ore from a stope which comprises forming amanway extending upwardly through the stope, drilling substantiallylaterally from the manway into the lower portion of the mass of unbrokenore in the stope, blasting the ore downwardly from the drill holes, andwithdrawing broken ore from the lower portion of the stope in controlledlimited amounts sufficient only to create voids in the mass of brokenore without lowering its upper surface substantially out of contact withthe lower surface of the still unbroken ore.

10. The method of mining ore from a stope which comprises forming amanway extending upwardly through the stope, maintaining the stopesubstantially full at all times of broken and unbroken ore with theupper surface of the column of broken ore in contact with the lowersurface of the unbroken ore, and conducting all ore-breaking operationsfrom working positions within the manway.

11. The method of mining ore from a deposit in ground requiring supportwhich comprises forming a substantially vertical column of broken ore ofconsiderable height within the deposit, forming a number of verticallyspaced ore chutes communicating with and intermediate the ends of thedeposit, withdrawing ore from said column through a rst of said chutesat a point well above the bottom of that part of the deposit to beworked, adding waste ll at the top of said column at substantially thesame rate as broken ore is withdrawn so as to maintain at all times afull column of broken material, discontinuing withdrawal of broken orethrough said first chute before the interface of broken ore and ll hassubsided to the level where the angle from the chute to the laterallymost remote part of said interface is less than about to the horizontal,breaking the ore of any barrier between said rst chute and the nextlower chute, and continuing withdrawal of the ore from said columnthrough said next lower chute.

12. The method of mining ore from a deposit in ground requiring supportwhich ccmprises breaking the ore throughout the height of an upper stopewithin the depcsit, forming an ore chute communicating with the bottomof the upper stope, withdrawing broken ore from said upper stope throughsaid chute and adding waste fill at the top of said stope as the uppersurface of broken ore subsides therein so that the stope is keptsubstantially full of broken material at all times, breaking the orethroughout the height of a second stope immediately below andcommunieating directly with said upper stope, discontinuing withdrawalof ore through the chute at the bottom of said upper'stope before theinterface of broken ore and ll has subsided to the level where the anglefrom said chute to the laterally most remote part of said interface isless than about 70 to the horizontal, forming a second chute at thebottom of said second stope and making further withdrawals of broken orethrough said chute at the bottom of said second stope.

13. In extracting ore from a deposit in which a column of ore has beenbroken and is being withdrawn by gravity flow through a chute, and wherewaste ll is added at the top of said column as the upper surface of thebroken ore subsides, the improvement which comprises discontinuingwithdrawal of the broken ore through' the chute before the interfacebetween the broken ore and ll has subsided to the level where the anglefrom said chute to the laterally most remote part of said interface isless than about 70 to the horizontal, forming a second chute incommunication with said column of ore and located at a point such thatthe angle between said second chute and the part of the interfacelaterally most remote from said second chute is appreciably greater thanabout 70, and making any further withdrawals of ore by gravity flowthrough said second chute.

PHILIP B. BUCKY.

REFERENCES CITED The following references are of record in the le ofthis patent:

Mining Engineers Handbook (3rd Ed. 1941), by Robert Peele, published byJohn Wiley & Sons, Inc., section 10-I pages 287, 290, 291, 292, 359 and360.

